Pharmacology · Class
Direct vasodilators !
Medicines that relax the muscle of blood vessels directly. They lower blood pressure strongly but trigger a fast heart rate and fluid retention.
Updated 2026-11-01
What they are
Drugs that act on vascular smooth muscle itself rather than on hormones or nerves: hydralazine and minoxidil dilate arterioles; sodium nitroprusside, an intravenous nitric oxide donor, dilates arteries and veins and is used in hypertensive emergencies.
Mechanism of action
Hydralazine relaxes arteriolar muscle by a mechanism not fully understood; minoxidil, through minoxidil sulfate, opens ATP-sensitive potassium channels; nitroprusside releases nitric oxide, which activates guanylyl cyclase and raises cGMP. The fall in pressure triggers the baroreflex (tachycardia) and the renin system (salt and water retention).
Target: Vascular smooth muscle: potassium channels (minoxidil), soluble guanylyl cyclase (nitroprusside)
Drugs in this class
- HydralazineA vasodilator that relaxes the arterioles. It is used intravenously in severe hypertension of pregnancy and, with a…Arteriolar smooth muscle (molecular target not fully established)
- Sodium nitroprussideAn intravenous nitric oxide donor for hypertensive emergencies. It works within minutes but releases cyanide, so it…Soluble guanylyl cyclase (activated by the nitric oxide it releases)
- MinoxidilA powerful oral vasodilator kept for severe, resistant hypertension. It is given with a beta blocker and a diuretic…ATP-sensitive potassium channel of vascular smooth muscle (SUR2 subunit)
Others in the class
- Diazoxide
- Dihydralazine
Test yourself
Think of the answer, then tap the question to see it.
Why are hydralazine and minoxidil usually given with a beta blocker and a diuretic?
The fall in pressure activates the baroreflex (tachycardia, angina) and the renin-angiotensin-aldosterone system (salt and water retention); the other two drugs block these responses.
Which toxic product does sodium nitroprusside release?
Cyanide, which the body turns into thiocyanate; both can accumulate with long infusions or organ failure.
Which direct vasodilator causes excess body hair, and how does it act?
Minoxidil: its sulfate metabolite opens ATP-sensitive potassium channels in arteriolar smooth muscle.
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - HYDRALAZINE HYDROCHLORIDE tablet (DailyMed (U.S. National Library of Medicine), 2026); DailyMed - SODIUM NITROPRUSSIDE injection, solution, concentrate (DailyMed (U.S. National Library of Medicine), 2026); DailyMed - MINOXIDIL tablet (DailyMed (U.S. National Library of Medicine), 2026); Farmacología básica y clínica (Katzung), cap. 11 (McGraw Hill, 2025).
Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake
Representative model, for educational purposes only.